Generally speaking, there are two basic techniques for introducing injectable medicament into the spinal area of a patient. The techniques both can be used to create spinal anesthesia, one being delivery of the medicament into the epidural space, "epidural," and the other, penetration of the dural membrane with delivery of the medicament into the subarachnoid space, "spinal" or "subarachnoid." The medicaments can be any type of liquid therapeutic material including antibiotics, steroids and the like, but generally are agents used for anesthesia and analgesia. When the liquid medicament is an anesthetic agent, a subarachnoid placement is recognized as providing a faster, more uniform distribution, but several major side effects may result from an improper subarachnoid placement. These side effects may include nerve damage, either from contact with the needle or from high local concentrations of the medicament, pooling or inadequate mixing of the medicament in the cerebrospinal fluid.
Delivery of the medicament into the subarachnoid space requires a penetration depth of several centimeters. Puncture of the dural membrane for introduction of a needle or catheter with a large gauge needle may result in postoperative leakage of cerebrospinal fluid from the puncture site, often resulting in severe postoperative headaches. Thus, when puncture of the dural membrane is made with a needle, the smaller the size of the puncture the lower the probability of post-procedural leakage of cerebrospinal fluid. Small diameter needles of the length required to enter the subarachnoid space are quite flexible and as a result, difficult to accurately position when making penetrations to a depth of several centimeters. Practitioners have recognized the need to use a needle with sufficient stiffness to make the initial penetration and the need to use a small diameter needle for penetration of the dural membrane. This recognition has evolved into the use of an eight to ten centimeters long, larger diameter (ca. 16-18 gauge) introducer needle to enter the epidural space followed by the use of the bore of the introducer needle to place a longer, i.e., twelve to sixteen centimeters long, smaller diameter (ca. 22-28 gauge) spinal needle adjacent to and then to penetrate the dural membrane. The spinal needle is then used to administer a bolus of the anesthetic agent. The bolus results in rapid onset of anesthesia, and depending upon the placement and the amount administered, the effect may last several hours.
Correct placement and delivery of a subarachnoid medicament is recognized by practitioners as being one of the more technique sensitive procedures currently practiced. There is considerable anatomical variation between patients related to the patient's size and weight. The practitioner generally positions the introducer needle between the vertebrae into the epidural space adjacent the dural membrane (dura), then advances the spinal needle through the dura membrane into the subarachnoid space. Accurately perceiving when the dura has been penetrated is often difficult for the practitioner. There are several widely practiced techniques to confirm that the needle has entered the subarachnoid space. Some practitioners depend upon feeling a "pop" as the spinal needle penetrates the dura. Other practitioners routinely place a drop of fluid on the proximal hub of the spinal needle and depend upon observing the drop being drawn into the hub when the dura is penetrated. Many practitioners also often confirm that the subarachnoid space is penetrated by using the spinal needle to withdraw a sample of cerebrospinal fluid.
A survey of previous patent literature reports in this general area is found in U.S. Pat. No. 5,085,631. The patent discloses a method for placement of a subarachnoid catheter that utilizes a three component apparatus comprising an outer needle, an inner needle and a catheter intermediate the two needles.
A recent U.S. pat., No. 5,312,375, discloses a set for spinal anesthesia that includes a spinal needle, a stylet, an introducer needle through which the spinal needle is introduced and a clamp for fixing the spinal needle for fixing the spinal needle to the introducer needle to stabilize the spinal needle. The patent teaches that the tube portion of the introducer needle protrudes proximally beyond the introducer needle hub so that a regulating device with a thumb screw or a toothed member can engage both the introducer needle and the spinal needle to fix the position of the spinal needle relative to the introducer needle. Generally, the introducer needle is an epidural needle. As disclosed in U.S. Pat. No. 5,312,375, the introducer needle cannot function as a conventional epidural needle, because the fluid path of the epidural needle is not fluid tight to a fluid handling attachment at the hub of the needle.
U.S. Pat. No. 5,584,820, discloses a variant of the regulating device disclosed in U.S. Pat. No. 5,312,375 for adjusting the length of a combined spinal epidural needle and the method of practicing its use. The disclosed invention utilizes standard commercially available spinal and epidural needles, adding a fixture for preselecting the spinal needle projection with respect to the epidural needle when the spinal needle is coaxially placed within the epidural needle. While this regulating device and method may be quite useful in the practice of combined spinal epidural medication, the use of this device disclosed in U.S. Pat. No. 5,584,820 adds an additional item to the procedure kit, and additional manipulations. Additionally, neither of these variants teach that the attachment between the spinal needle and the epidural needle forms a fluid tight seal, thus, leakage of medicament or cerebrospinal fluid between the spinal needle and the epidural needle may occur.
Subarachnoid placement of medicaments, if done properly, is recognized as desirable. Thus, a device and a method for its use that would minimize the size of the puncture of the dural membrane, allow accurate and controlled placement of a therapeutically effective amount of a medicament within the subarachnoid space, thereby reducing the potential for nerve damage, coupled with an ability to rapidly initiate and maintain a therapeutic level of the medicament for longer procedures would represent an advance to the medical arts. If such an epidural needle that facilitated the subarachnoid placement that was fully functional as a standard epidural needle the art would be further advanced. A method and apparatus that addresses these needs constitute the present invention.